Altered RET gene mRNA expression in Hirschsprung's disease

Translational research in Hirschprung's disease at the National Children's Research Centre in Dublin

Hirschsprung's disease (HD) is a congenital condition characterised by aganglionosis in the distal bowel. Over the years, at the National Children's Research Centre (NCRC), HD has been one of the most prominent and successful research areas for Prof. Prem Puri's research team. Research fellows from around the world came to the NCRC to work on both animal and human studies of HD and, cumulatively, made important discoveries in this field, publishing a total of 144 HD articles in peer-reviewed journals. Through their published work, the NCRC has been recognised as the leading international centre for the investigation of HD and its allied disorders. In this review, I will summarise the main findings from this work.

Knockout mouse models of Hirschsprung's disease

PURPOSE

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cell migration. Rodent animal models of aganglionosis have contributed greatly to our understanding of the genetic basis of HSCR. Several natural or target mutations in specific genes have been reported to produce developmental defects in neural crest migration, differentiation or survival. The aim of this study was to review the currently available knockout models of HSCR to better understand the molecular basis of HSCR.

METHODS

A review of the literature using the keywords "Hirschsprung's disease", "aganglionosis", "megacolon" and "knockout mice model" was performed. Resulting publications were reviewed for relevant mouse models of human aganglionosis. Reference lists were screened for additional relevant studies.

RESULTS

16 gene knockout mouse models were identified as relevant rodent models of human HSCR. Due to the deletion of a specific gene, the phenotypes of these knockout models are diverse and range from small bowel dilatation and muscular hypertrophy to total intestinal aganglionosis.

CONCLUSIONS

Mouse models of aganglionosis have been instrumental in the discovery of the causative genes of HSCR. Although important advances have been made in understanding the genetic basis of HSCR, animal models of aganglionosis in future should further help to identify the unknown susceptibility genes in HSCR.

A meta-analysis of clinical outcome in patients with total intestinal aganglionosis

Total intestinal aganglionosis (TIA) is the most extreme and rare form of Hirschsprung disease (HD). Until few years ago TIA was considered to be a uniformly fatal condition. Survival has improved in the recent years with the advent of parenteral nutrition, innovative surgical techniques and small bowel transplantation. The purpose of this meta-analysis was to determine the clinical outcome of TIA following various surgical procedures. A meta-analysis of cases of TIA reported in the literature between 1985 and 2009 was performed. Detailed information was recorded regarding the extent of aganglionosis, surgical procedures performed and clinical outcome. In case of survivors, authors of reports were contacted to obtain the up-to-date clinical status of the patient. There were 68 cases of TIA reported worldwide, 40 (58.8%) males and 28 (41.2%) females. 6 (8.8%) patients had extension of aganglionosis up to the stomach, 19 (27.9%) up to the duodenum and 43 (63.2%) patients had aganglionosis up to 20 cm below the duodeno-jejunal flexure. Family history of HD was documented in 10 (14.7%) patients. RET-gene mutation were identified in 10 (71.4%) of the 14 patients investigated of RET germline mutations. Eleven patients (16.2%) died prior to surgical treatment, 25 patients (36.8%) only had jejunostomy, while 20 (29.4%) had Ziegler's myectomy-myotomy. 12 (17.6%) patients received intestinal transplantation (ITx) or combined liver-intestinal transplantation (LITx). Forty-five (66.2%) patients died at ages ranging from 1 day to 8 years. Twenty-three (33.8%) patients were alive; the longest survivor was 10 years old after LITx. Innovative surgical procedures and parenteral nutrition have improved clinical outcome of patients with TIA in recent years. Intestinal transplantation appears promising in the management of TIA.

Studies of RET gene expression and acetylcholinesterase activity in a series of sporadic Hirschsprung's disease

The purpose is to present the studies of RET gene expression and acetylcholinesterase activity in 23 patients operated for Hirschsprung's disease (HD). The patients underwent either transanal endorectal pull-through or Duhamell's procedure. Full-thickness intestinal samples from the three different segments (ganglionic, intermediate and aganglionic) were collected. Each tissue sample was divided in two portions, one for AChE histochemical staining and the other for examination of RET mRNA expression level. All patients had an uneventful postoperative recovery. In all patients, the AChE stainings demonstrated the absence of activity in the ganglionic area, the marked increase of positive fibers in the aganglionic area, and little increase of positive fibers in the intermediate area. In the ganglionic and intermediate areas, all patients (100%) showed significant RET gene expression. In the aganglionic area, 18 patients (78.3%) did not present gene expression and the other five patients (21.7%) presented gene expression that was similar to the ganglionic and intermediate areas. The results reinforce the conclusion that the method of AChE staining is effective for the diagnosis of intestinal aganglionosis and confirm the knowledge that genes beyond RET may be implicated in the genesis of sporadic cases of HD.

The relationship between expressions of the laminin gene and RET gene in Hirschsprung's disease

BACKGROUND

The cause of Hirschsprung's disease (HD) remains unclear, but currently there are two theories: the mutation of the RET gene and the change of enteric microenvironment. This study was undertaken to elucidate the cause of HD by assessing the expression of laminin (LN), laminin gene, and the RET gene in the aganglionic segment, transitional zone and normal segment of the colon in patients with HD.

METHODS

Specimens of the aganglionic segment, transitional zone, and normal segment of the colon from 27 cases of HD were stained immunohistologically by a PV 9000 polymer detection system. Photos were taken by the RS image system, and the staining area of each image was calculated by a JD 801 image analysis system. The qualitative expressions of the laminin gene and RET gene of these three segments in the 27 cases were detected by reverse transcription-polymerase chain reaction (RT-PCR), and the difference of the expressions was shown by the alpha 9900 image analysis system. The quantitative expressions of the laminin gene and RET gene in the three segments were detected by real-time quantitative PCR, and the difference of the expression was shown by SDS software.

RESULTS

The laminin and laminin gene were expressed in all the three segments. The expression was higher in the aganglionic segment than in the dilated segment, and the expression decreased stepwisely from the aganglionic segment to the normal segment, while the expression of the RET gene was opposite, showing an increased segmenting from the aganglionic segment to the normal segment. The correlation between the expressions of the two genes was negatively correlated.

CONCLUSIONS

The highly increased expression of LN in the aganglionic segment may cause early differentiation, early maturation and premature ecesis of enteric nervous cells. The change of the microenvironment of colon wall may be the cause of HD. The negative correlation between the expression of the two genes may be closely related to the occurrence of HD.

Stephen L. Gans Distinguished Overseas Lecture. The neural crest in pediatric surgery

AIM

This review highlights the relevance of the neural crest (NC) as a developmental control mechanism involved in several pediatric surgical conditions and the investigative interest of following some of its known signaling pathways.

METHODS

The participation of the NC in facial clefts, ear defects, branchial fistulae and cysts, heart outflow tract and aortic arch anomalies, pigmentary disorders, abnormal enteric innervation, neural tumors, hemangiomas, and vascular anomalies is briefly reviewed. Then, the literature on clinical and experimental esophageal atresia-tracheoesophageal fistula (EA-TEF) and congenital diaphragmatic hernia (CDH) is reviewed for the presence of associated NC defects. Finally, some of the molecular signaling pathways involved in both conditions (sonic hedgehog, Hox genes, and retinoids) are summarized.

RESULTS

The association of facial, cardiovascular, thymic, parathyroid, and C-cell defects together with anomalies of extrinsic and intrinsic esophageal innervation in babies and/or animals with both EA-TEF and CDH strongly supports the hypothesis that NC is involved in the pathogenesis of these malformative clusters. On the other hand, both EA-TEF and CDH are observed in mice mutant for genes involved in the previously mentioned signaling pathways.

CONCLUSIONS

The investigation of NC-related molecular pathogenic pathways involved in malformative associations like EA-TEF and CDH that are induced by chromosomal anomalies, chemical teratogens, and engineered mutations is a promising way of clarifying why and how some pediatric surgical conditions occur. Pediatric surgeons should be actively involved in these investigations.

Pathogenesis of Hirschsprung's disease and its variants: recent progress

The enteric nervous system (ENS) is a complex network of interconnected neurons within the wall of the intestine that controls intestinal motility, regulates mucosal secretion and blood flow, and also modulates sensation from the gut. The cells that form the ENS in mammals are derived primarily from vagal neural crest cells. During the past decade there has been an explosion of information about genes that control the development of neural crest. Molecular-genetic analysis has identified several genes that have a role in the development of Hirschsprung's disease. The major susceptibility gene is RET, which is also involved in multiple endocrine neoplasia type 2. Recently, genetic studies have provided strong evidence in animal models that intestinal neuronal dysplasia (IND) is a real entity. HOX11L1 knockout mice and endothelin B receptor-deficient rats demonstrated abnormalities of the ENS resembling IND type B in humans. These findings support the concept that IND may be linked to a genetic defect.

Cell-line specific chromatin acetylation at the Sox10-Pax3 enhancer site modulates the RET proto-oncogene expression

The RET gene is expressed with high tissue and stage specificity during development. Understanding its transcriptional regulation might provide new clues to clarify developmental mechanisms. Here we show that the histone deacetylase inhibitor sodium butyrate (NaB) increases RET transcription in cells displaying low levels of its mRNA, while it has no effect in cells expressing at high levels. Chromatin immunoprecipitation (ChIP) experiments showed increased histone acetylation within the 5' flanking [corrected] region, in particular the Sox10-Pax3 enhancer site, due to NaB. Accordingly, ChIP showed different acetylation levels at the Sox10-Pax3 site associated with cell-line specific RET transcription rates. Concluding, chromatin acetylation targeted to functional sequences in the RET regulatory region may control its transcription.

Expression of RET proto-oncogene and GDNF deficit in Hirschsprung's disease

PURPOSE

The aim of this study was to investigate GDNF (glial cell line-derived neurotrophic factor) protein expression and RNA expression level of the RET proto-oncogene in human aganglionic (AG) bowel in Hirschsprung's disease (HD) and to further understand the pathophysiology of HD.

METHODS

To evaluate the possible implication of the RET gene and GDNF for the development of HD, mRNA expression level of the RETgene was examined by using the reverse transcription-polymerase chain reaction (RT-PCR) technique and protein expression level of the GDNF using an immunohistochemical technique in the bowel specimens of 15 HD patients.

RESULTS

A significantly less intense signal for RETmRNA was found in the AG bowel compared with the ganglionic bowel. In different age groups of patients, the intensities of RET level had similar results. In the same patients, there was strong GDNF immunoreactivity in the myenteric plexuse in ganglionic bowel. In the myenteron in AG bowel, the number of GDNF immunoreactive neuron cells was reduced significantly compared with normal ganglionic bowel.

CONCLUSIONS

From these preliminary data we conclude that the decreased RET expression in the AG bowel may suggest mal development of neural crest-derived cells in HD. The reduced level of GDNF in AG bowel may suggest a GDNF expression deficit interrupting the faithful signaling via RET, and both are implicated in the pathogenesis of HD.

Altered endothelin-3 and endothelin-B receptor mRNA expression in Hirschsprung's disease

BACKGROUND

Recently, the endothelin-3 (EDN3) and endothelin-B receptor (EDNRB) gene have been recognized as susceptibility genes for Hirschsprung's disease (HD). However, gene mutations have been observed only in limited cases, and the role of EDN3 in the pathogenesis and motility dysfunction in HD is not understood fully. To evaluate the possible implication of EDN3 and EDNRB for the development of HD, we examined the EDN3 and EDNRB mRNA level in bowel specimens of HD patients.

METHODS

Entire resected specimens of colon were obtained from 14 patients with HD. Eight age-matched control patients without gastroenteric disorders also were examined. mRNA was extracted from ganglionic and aganglionic segments of the HD specimens and normal colons. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of EDN3 and EDNRB mRNA.

RESULTS

In normal colon, constant EDN3 and EDNRB mRNA expression was observed. In HD, EDN3 and EDNRB mRNA expression was observed. In HD, EDN3 and EDNRB mRNA levels were decreased both in ganglionic and aganglionic segment in 2 cases. In 6 cases, EDN3 mRNA expression was decreased in aganglionic segment and in another 2 cases, EDNRB mRNA expression was decreased in aganglionic segment. In the remaining 4 cases, EDN3 and EDNRB mRNA levels were similar to controls.

CONCLUSION

The authors' findings indicate that loss of EDN3 and EDNRB function may be involved in the maldevelopment of neural crest-derived cells causing HD in many patients.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

Reduced glial cell line-derived neurotrophic factor level in aganglionic bowel in Hirschsprung's disease

BACKGROUND/PURPOSE

Glial cell line-derived neurotrophic factor (GDNF) is suggested to be essential for the development of the enteric nervous system. The aim of this study was to investigate GDNF protein expression in human aganglionic (AG) bowel in Hirschsprung's disease (HD) using immunofluorescence and enzyme-linked immunosorbent assay (ELISA) analysis, to further understand the pathophysiology of HD.

METHODS

Colonic specimens were obtained from eight patients with HD (aged 7 days to 14 months) at the time of definite pull-through surgery, including both normoganglionic (NG) and aganglionic (AG) segments. Immunofluorescence was performed using anti-GDNF polyclonal antibody and FITC-conjugated secondary antibody on the formalin-fixed and paraffin-embedded specimens. For ELISA analysis, specimens were homogenized by adding 10 volumes of 10-mmol/L phosphate-buffered saline containing proteinase inhibitors. Centrifuged supernatant was used for the quantitative analysis using sandwich-type ELISA for human GDNF.

RESULTS

There was strong GDNF immunoreactivity in the mucosal epithelium, submucosal and myenteric plexuses, and hypertrophic nerve trunks. In the mucosa in AG bowel, the number of GDNF immunoreactive epithelial cells was significantly reduced compared with NG bowel (mean +/- SD, AG/NG = 227.2 +/- 73.1/310.8 +/- 80.5 GDNF immunoreactive cells per 100 crypts, P < .05). Using ELISA, the level of GDNF in full-thickness bowel was reduced significantly in AG bowel compared with NG bowel (mean +/- SD, AG/NG = 860.2 +/- 309.8/1777.5 +/- 271.4 pg/g wet tissue, P < .001).

CONCLUSION

Because GDNF is essential for the development of the enteric nervous system, our findings of reduced level of GDNF in AG bowel as well as reduced number of GDNF immunoreactive cells in the mucosa of AG bowel suggest that GDNF may play an important role in the pathogenesis of HD.

Altered mRNA expression of the neuronal nitric oxide synthase gene in Hirschsprung's disease

Nitric oxide has been described as an inhibitory neurotransmitter to mediate smooth muscle relaxation in the mammalian gastrointestinal tract. The enzyme neuronal nitric oxide synthase (NOS) catalyzes the formation of NO. The authors examined the expression of neuronal NOS gene at the mRNA level in intestinal specimens from seven patients who had Hirschsprung's disease (HD) using reverse transcription polymerase chain reaction (RT-PCR) technique. With 35 cycles of PCR reaction, substantial signals of neuronal NOS mRNA were observed in the ganglionic bowel in all seven patients, whereas in the aganglionic bowel, neuronal NOS signals were weak in three patients, and undetectable in four patients. By increasing the PCR cycle to 40 cycles, barely detectable signals were observed in two of the latter four patients. Semiquantitative analysis in the three patients who showed weak signals with 35 cycles of PCR indicated that neuronal NOS mRNA expression in aganglionic bowel was decreased at least 1/50 to 1/100 of the level expressed in ganglionic bowel. Because absence or low level of expression of neuronal NOS mRNA may lead to impaired production of NO, our observations suggest that motility dysfunction in HD may be as a result of markedly decreased or no expression of the neuronal NOS gene at the mRNA level.

The RET proto-oncogene: a challenge to our understanding of disease pathogenesis

RET gene alterations as disease-causative mutations have been demonstrated in five different disease entities: Hirschsprung's disease (HD); papillary thyroid carcinoma; and three types of inherited cancer syndromes: multiple endocrine neoplasia (MEN) 2A, MEN 2B, and familial medullary thyroid carcinoma. RET is expressed during embryogenesis in a temporally and spatially regulated manner, and plays an important role in the normal development of a variety of cell lineages, particularly in the establishment of the enteric nervous system. RET mutations observed in patients with HD are scattered along the gene without any hot spots, and possess a loss-of-function effect. RET mutations are detected with a higher incidence among familial cases (50%) than sporadic cases (15%-20%), and are more closely associated with long-segment HD than short-segment disease. In contrast to HD mutations, missense mutations observed in MEN 2 syndromes occur at specific codons, and gene rearrangements are characteristic in papillary thyroid carcinoma. Both missense mutations and gene rearrangements act in a dominant fashion, and cause constitutive phosphorylation on the tyrosine of RET and highly enhance RET kinase activity, leading to transforming or oncogenic activity.